Question

When red light passing through a convex lens is replaced by light of blue colour, how will the focal length of the lens change?

Answer 1

focal length inversely proportional to refractive index
nd refractive index is inversely proportional to wavelength
so focal length is directly proportional to wavelength.....
hope it helps

Answer 2

Focal length is directly proportional to wavelength.

Since , wavelength of blue is lesser than red , focal length will decrease .